Joshua D. Batson, Daniel A. Spielman, Nikhil Srivastava. Twice-ramanujan sparsifiers. In Michael Mitzenmacher, editor, Proceedings of the 41st Annual ACM Symposium on Theory of Computing, STOC 2009, Bethesda, MD, USA, May 31 - June 2, 2009. pages 255-262, ACM, 2009. [doi]
Abstract is missing.